Minor Connectors & Rests

Minor Connectors & Minor Connectors & RestsRests

Rola M. Shadid, BDS, MScRola M. Shadid, BDS, MSc

Lecture OutlineLecture Outline

Discuss functions of minor Discuss functions of minor connectorconnector

Discuss types of minor connectorsDiscuss types of minor connectors Discuss functions of restsDiscuss functions of rests Discuss forms of rests & prep of Discuss forms of rests & prep of

rest seatsrest seats

Minor ConnectorsMinor Connectors Connects components to the major Connects components to the major

connectorconnector– Direct retainerDirect retainer– Indirect retainerIndirect retainer– Denture baseDenture base

Functions of Minor Functions of Minor ConnectorsConnectors

Unification and rigidityUnification and rigidity Stress distribution Stress distribution * * Bracing through contact with Bracing through contact with

guiding planesguiding planes Maintain a path of insertion via Maintain a path of insertion via

contact with guiding planescontact with guiding planes

Types of Minor ConnectorsTypes of Minor Connectors

Embrasure Minor ConnectorsEmbrasure Minor Connectors– Between two adjacent teethBetween two adjacent teeth

Embrasure Minor ConnectorsEmbrasure Minor Connectors

Should have sufficient Should have sufficient bulk to be rigid but in the bulk to be rigid but in the same time unobjectionable same time unobjectionable as possibleas possible

Should be located in an Should be located in an embrasure not be located embrasure not be located on a convex surfaceon a convex surface

Should be tapering toward Should be tapering toward the contact areathe contact area


– Joins major connector at right angles Joins major connector at right angles – Relief placed so connector not directly on Relief placed so connector not directly on

soft tissuesoft tissue


It should be thickest It should be thickest toward the lingual toward the lingual surface, tapering surface, tapering toward the contact toward the contact areaarea

Triangular shaped in Triangular shaped in cross section cross section

Embrasure Minor Embrasure Minor ConnectorsConnectors

– Contact teeth Contact teeth above height of above height of contour contour

– Prevents wedging Prevents wedging & tooth mobility& tooth mobility

Gridwork Minor ConnectorsGridwork Minor Connectors

Connect the denture base and teeth Connect the denture base and teeth to the major connectorto the major connector

Gridwork Minor ConnectorsGridwork Minor Connectors Adjacent edentulous spaces Adjacent edentulous spaces Usually connect major connector Usually connect major connector

to direct retainersto direct retainers Open lattice work or mesh typesOpen lattice work or mesh types

Minor connector for Minor connector for mandibular distal mandibular distal extension base extension base should extend should extend posteriorly about posteriorly about 2/3 2/3 the length of the the length of the edentulous ridgeedentulous ridge

Never on the Never on the ascending portion ascending portion of the ridge of the ridge


Minor connectors Minor connectors for maxillary for maxillary distal extension distal extension denture bases denture bases should extend the should extend the entire length of entire length of the residual ridgethe residual ridge


Gridwork Minor ConnectorsGridwork Minor Connectors Mesh type Mesh type

– FlatterFlatter– Potentially more rigidPotentially more rigid– Less retention for acrylic Less retention for acrylic

if openings are smallif openings are small

Gridwork Minor ConnectorsGridwork Minor Connectors Lattice TypeLattice Type

• Potentially superior retentionPotentially superior retention• Interferes with setting of teeth, if Interferes with setting of teeth, if

struts are too thickstruts are too thick

– Both types are acceptable if correctly Both types are acceptable if correctly designeddesigned

Gridwork ReliefGridwork Relief Mechanical retention of denture Mechanical retention of denture

base resinbase resin Allows the acrylic resin to flow Allows the acrylic resin to flow

under the gridworkunder the gridwork

Gridwork ReliefGridwork Relief Relief wax is placed in the Relief wax is placed in the

edentulous areas edentulous areas 1 mm of relief1 mm of relief

Relief Under the GridworkRelief Under the Gridwork

Should begin 1.5 - 2 mm Should begin 1.5 - 2 mm from the abutment toothfrom the abutment tooth

Relief Under the GridworkRelief Under the Gridwork Creates a metal to tissue contactCreates a metal to tissue contact

– Preferable since it wears lessPreferable since it wears less– Less porous, (hygiene)Less porous, (hygiene)

Junction With Major ConnectorJunction With Major Connector

Butt joint with slight undercut in metalButt joint with slight undercut in metal Maximum bulk of the acrylic resinMaximum bulk of the acrylic resin Prevents thin, weak edges fracturing Prevents thin, weak edges fracturing

a

major connector

edentulous ridge

butt joint slight undercut

a

incorrect (>90° joint)

Gridwork DesignGridwork Design

Facially just over the crest of the residual ridge

Position of Major Connector JunctionPosition of Major Connector Junction

Should be ≈ 2 mm medial to lingual Should be ≈ 2 mm medial to lingual surface of denture teethsurface of denture teeth

Ensures bulk of resin around teethEnsures bulk of resin around teeth

Mandibular Tissue StopsMandibular Tissue Stops Contact of metal with Contact of metal with

cast at posterior of cast at posterior of distal extension distal extension gridworkgridwork

Prevents distortion at Prevents distortion at free end during free end during hydraulic pressure of hydraulic pressure of processingprocessing

No Tissue Stops In MaxillaNo Tissue Stops In Maxilla

Maxillary major Maxillary major connector acts as a connector acts as a tissue stop (no relief)tissue stop (no relief)

Proximal PlatesProximal Plates Minor connectors originating from the Minor connectors originating from the

gridwork in an edentulous areagridwork in an edentulous area Broad contact with guiding planesBroad contact with guiding planes May or may not terminate in an occlusal restMay or may not terminate in an occlusal rest

Proximal PlatesProximal Plates


Shifted slightly lingually Shifted slightly lingually – Increases rigidityIncreases rigidity– Enhances reciprocationEnhances reciprocation– Improves Improves estheticsesthetics

Often a triangular space below the Often a triangular space below the guiding plane (an undercut)guiding plane (an undercut)


Rigid, cannot be Rigid, cannot be placed in undercutplaced in undercut

Block-outBlock-out placed in placed in undercuts prior to undercuts prior to waxing and casting waxing and casting the frameworkthe framework

Rests & Rest SeatsRests & Rest Seats

o The most effective The most effective resistance can be resistance can be provided if the provided if the tooth is stressed tooth is stressed along its long axisalong its long axis

o Prosthesis should Prosthesis should engage the tooth in engage the tooth in a manner that a manner that encourages axial encourages axial loadingloading

RestRest A rigid component of RPD resting in a A rigid component of RPD resting in a

recessed preparation on the occlusal, recessed preparation on the occlusal, lingual or incisal surface of a tooth.lingual or incisal surface of a tooth.

Provides vertical supportProvides vertical support

Rest SeatRest Seat

Portion of a tooth prepared to Portion of a tooth prepared to receive a rest *receive a rest *

FunctionsFunctions

Direct occlusal forces along Direct occlusal forces along long axis of abutmentlong axis of abutment

FunctionsFunctions

SUPPORT - Prevents SUPPORT - Prevents impingement of soft tissue *impingement of soft tissue *

Slides down inclineSlides down incline

Fractured abutment, no rest seat

Major connector imbeds into tissue

FunctionsFunctions Maintains established Maintains established

occlusal relationships by occlusal relationships by preventing settling of the preventing settling of the denture *denture *

FunctionsFunctions Maintain components in their Maintain components in their

planned positions (maintains planned positions (maintains a clasp -tooth relationship)a clasp -tooth relationship)

FunctionsFunctions Provide reference for relines or Provide reference for relines or

impressionsimpressions

FunctionsFunctions Act as indirect retainerAct as indirect retainer

– Prevents rotation (Class I or II Prevents rotation (Class I or II RPD’s only)RPD’s only)

Form of Occlusal RestForm of Occlusal Rest

Rounded Rounded triangular shape triangular shape with the apex with the apex toward center of toward center of occlusal surfaceocclusal surface

As long as it is As long as it is widewide

Occlusal Rest Seat FormOcclusal Rest Seat Form Base of triangle should be one Base of triangle should be one

third the bucco-lingual width third the bucco-lingual width of the tooth *of the tooth *

Rest Seat FormRest Seat Form Smooth flowing outline form Smooth flowing outline form

(i.e. no sharp line angles)(i.e. no sharp line angles)

Occlusal Rest SeatOcclusal Rest Seat Deepest portion is centralDeepest portion is central

Occlusal Rest SeatOcclusal Rest Seat Floor should be apical Floor should be apical

to marginal ridge to marginal ridge Angle formed by Angle formed by

occlusal rest & occlusal rest & vertical minor vertical minor connector from which connector from which it originates should be it originates should be less than 90°less than 90°

““Positive” Rest SeatsPositive” Rest Seats

An explorer tip will not slide An explorer tip will not slide off the rest seatoff the rest seat

a

Explorer willNOT slip off rest

seat if pulledproximallly

Explorer WILLslip off rest seat

if pulledproximallly

‘Positive’ Rest Seat(< 90°)

Rest Seat not ‘Positive’(>90°)

Occlusal Rest SeatOcclusal Rest Seat Directs the occlusal forces along the Directs the occlusal forces along the

long axis of the toothlong axis of the tooth Prevent orthodontic movementPrevent orthodontic movement

Occlusal Rest SeatOcclusal Rest Seat

Floor should be concave or Floor should be concave or spoon shaped (ball-&-socket spoon shaped (ball-&-socket joint)joint)

Prevents horizontal stresses Prevents horizontal stresses & torque& torque

Occlusal Rest Seat Occlusal Rest Seat Marginal ridge must be lowered Marginal ridge must be lowered

and rounded 1-1.5mmand rounded 1-1.5mm– Bulk of metal to prevent Bulk of metal to prevent

fracture *fracture *

Occlusal Rest SeatOcclusal Rest Seat Adjacent ToothAdjacent Tooth

– Rest not flared to facial line Rest not flared to facial line angleangle

– Lingual flared more - space for Lingual flared more - space for minor connectorminor connector

Secondary Occlusal Rest *Secondary Occlusal Rest *

To prevent slippage of To prevent slippage of the primary rest the primary rest

To prevent To prevent orthodontic movementorthodontic movement

of abutment toothof abutment tooth To direct forces over To direct forces over

greatest root mass of greatest root mass of abutmentabutment

Extended Occlusal Rest *Extended Occlusal Rest *

To minimize further To minimize further tipping of the abutment tipping of the abutment

To ensure that forces are To ensure that forces are directed down the long directed down the long axis of abutmentaxis of abutment

Extended Occlusal RestExtended Occlusal Rest Extends more than one Extends more than one

half mesiodistal width of half mesiodistal width of toothtooth

One third the One third the buccolingual width of buccolingual width of the tooth the tooth

Allow for minimum of 1 Allow for minimum of 1 mm thickness of metalmm thickness of metal

Rounded with no Rounded with no undercutsundercuts

Extended Occlusal RestExtended Occlusal Rest (Onlay)(Onlay)

If the abutment is If the abutment is severely tilted, the severely tilted, the extended occlusal rest extended occlusal rest may take the form of may take the form of

an onlayan onlay to restore to restore the occlusal planethe occlusal plane

Extended Occlusal RestExtended Occlusal Rest (Onlay) *(Onlay) *

Provide Provide stabilizationstabilization

Restore the Restore the contour & contour & occlusion of occlusion of natural toothnatural tooth

Directs forces Directs forces down the long axis down the long axis of tooth of tooth

Double Embrasure Double Embrasure (Interproximal) Rest Seat(Interproximal) Rest Seat Adjacent rests are Adjacent rests are

used to prevent used to prevent interproximal interproximal wedging by wedging by frameworkframework

Joined rests are Joined rests are designed to shunt designed to shunt food away from food away from contact pointscontact points

Double Embrasure Double Embrasure (Interproximal) Rest Seat Form(Interproximal) Rest Seat Form

Flared more dramatically on facial Flared more dramatically on facial and lingual line angles *and lingual line angles *

Interproximal Rest Seat Prep.Interproximal Rest Seat Prep. Avoid reducing or Avoid reducing or

eliminating contact eliminating contact points of abutment points of abutment teethteeth

Sufficient tooth Sufficient tooth structure must be structure must be removed removed **

Ensure all line Ensure all line angles are smoothedangles are smoothed

Prep. For Rest SeatsPrep. For Rest Seats

Rests may be placed on sound Rests may be placed on sound enamel or on any restoration enamel or on any restoration materialmaterial

Rests placed on sound enamel are Rests placed on sound enamel are not conducive to caries in mouth not conducive to caries in mouth with a low-caries index provided with a low-caries index provided that good oral hygiene is that good oral hygiene is maintainedmaintained

Prep. for Rest SeatsPrep. for Rest Seats

Patient should be advised that Patient should be advised that future susceptibility to caries future susceptibility to caries is not predictable and that is not predictable and that much depends on oral hygiene much depends on oral hygiene and possible future changes in and possible future changes in caries susceptibility.caries susceptibility.


A fluoride gel should be applied A fluoride gel should be applied to abutment teeth following to abutment teeth following enamel recontouringenamel recontouring

If the master cast will be If the master cast will be fabricated from an irreversible fabricated from an irreversible hydrocolloid impression, hydrocolloid impression, application of the gel should be application of the gel should be delayed until after impressions delayed until after impressions are made.are made.


Light pressure Light pressure High-speed handpieceHigh-speed handpiece +/- Waterspray+/- Waterspray Minimal heat is generatedMinimal heat is generated


Keep in enamelKeep in enamel No anesthesiaNo anesthesia

Prep. for Occlusal Rest SeatsPrep. for Occlusal Rest Seats

The larger round bur is The larger round bur is used first to lower the used first to lower the marginal ridge and to marginal ridge and to establish the outline establish the outline form of rest seatform of rest seat

A slightly smaller round A slightly smaller round bur is then used to bur is then used to deepen floor of rest seatdeepen floor of rest seat

The preparation is The preparation is smoothed by polishing smoothed by polishing pointpoint


When a small enamel defect is When a small enamel defect is encountered in the encountered in the preparation of an occlusal rest preparation of an occlusal rest seat, it is usually best to ignore seat, it is usually best to ignore it until the rest preparation it until the rest preparation has been completed.has been completed.


When perforation in When perforation in restoration does occur, it may restoration does occur, it may be repaired, but occasionally be repaired, but occasionally the making of a new the making of a new restoration is unavoidable.restoration is unavoidable.

Occlusal Rest Seats in CrownsOcclusal Rest Seats in Crowns

Occlusal rest seats in Occlusal rest seats in crowns and inlays crowns and inlays are generally made are generally made somewhat somewhat larger larger and deeper and deeper than than those in enamel *those in enamel *

Lingual Rests on Canines & Lingual Rests on Canines & Incisor TeethIncisor Teeth

A canine is much preferred over A canine is much preferred over incisor *incisor *

When a canine is not present, When a canine is not present, multiple rests that are spread over multiple rests that are spread over several incisors are preferable to several incisors are preferable to the use of the use of

single incisorsingle incisor

Cingulum Rest Seat FormCingulum Rest Seat Form Inverted “V” at junction of gingival & middle one third of toothInverted “V” at junction of gingival & middle one third of tooth < 90< 9000

Cingulum Rest Seat FormCingulum Rest Seat Form

Rest seat prep. broadest at Rest seat prep. broadest at most lingual aspect of most lingual aspect of caninecanine

As preparation approaches As preparation approaches proximal surfaces of tooth, proximal surfaces of tooth, it is less broad than at any it is less broad than at any other areasother areas

Cingulum Rest Seat FormCingulum Rest Seat Form Slightly rounded to avoid sharp line Slightly rounded to avoid sharp line

anglesangles Test as ‘positive’ with explorer tipTest as ‘positive’ with explorer tip

(floor of (floor of rest seat should be toward cingulum rest seat should be toward cingulum

rather than rather than axial wall)axial wall)

Cingulum Rest SeatCingulum Rest Seat

2.5 to 3 mm2.5 to 3 mmmesiodistal lengthmesiodistal length

2 mm 2 mm labiolingual widthlabiolingual width

1. 5 mm1. 5 mm incisal-apical depth incisal-apical depth **

Correct PreparationCorrect Preparation

Preparation Too HighPreparation Too High

Preparation Too LowPreparation Too Low

Cingulum Rest Prep.Cingulum Rest Prep. Do not create an enamel Do not create an enamel

undercutundercut Cylindrical bur along the long Cylindrical bur along the long

axis of the toothaxis of the tooth

Maxillary Cingulum Rest Maxillary Cingulum Rest SeatsSeats Avoid opposing occlusion Avoid opposing occlusion

Maxillary Cingulum Rest Maxillary Cingulum Rest SeatsSeats

1.5 - 2.0 mm clearance for 1.5 - 2.0 mm clearance for metal metal

Check with articulated Check with articulated models *models *

Cingulum Rest Seat PlacementCingulum Rest Seat Placement Place in sound tooth structurePlace in sound tooth structure** Not on amalgam restorationsNot on amalgam restorations If cingulun not prominent or large pulpIf cingulun not prominent or large pulp

– Use different toothUse different tooth– Composite restorationComposite restoration– Onlay or crownOnlay or crown– Bonded rest seatBonded rest seat

Bonded Rest SeatBonded Rest Seat

Cast chromium-cobalt Cast chromium-cobalt alloy rest seat forms alloy rest seat forms

Attached to lingual Attached to lingual surfaces of anterior surfaces of anterior teeth by use of teeth by use of composite resin composite resin cements with acid-cements with acid-etched tooth prep.etched tooth prep.

Ball (Round) Lingual RestBall (Round) Lingual Rest

Mesial of the canine teeth when Mesial of the canine teeth when typical cingulum rest contraindicatedtypical cingulum rest contraindicated– Large restorationLarge restoration– Lack of clearance Lack of clearance with the opposing teethwith the opposing teeth– Poor cingulumPoor cingulum

Ball (Round) Lingual RestBall (Round) Lingual Rest

Spoon shaped, similar to occlusal rest seatSpoon shaped, similar to occlusal rest seat More difficult due to the incline of the More difficult due to the incline of the

lingual surface lingual surface Easily incorporated into crownsEasily incorporated into crowns

Ball (Round) Lingual RestsBall (Round) Lingual Rests Rest seats prep. in Rest seats prep. in -tooth surface if sufficient -tooth surface if sufficient

enamel thickness existsenamel thickness exists -restorations placed in teeth where -restorations placed in teeth where

enamel thickness is inadequateenamel thickness is inadequate

More conservative than cingulum More conservative than cingulum lingual rest seatslingual rest seats

Incisal RestIncisal Rest The least desirable placement of The least desirable placement of

a rest seata rest seat Incisal rests are used Incisal rests are used

predominantly predominantly as as - Auxiliary rests - Auxiliary rests - Indirect retainers- Indirect retainers

Incisal RestIncisal Rest

Lingual Rest Preferable to Lingual Rest Preferable to Incisal Rest Incisal Rest

Lingual rest placed nearer Lingual rest placed nearer horizontal axis of rotation horizontal axis of rotation (tipping axis) of abutment (tipping axis) of abutment

- Less tendency to tip the tooth *- Less tendency to tip the tooth * More esthetically acceptable More esthetically acceptable

than incisal restthan incisal rest

Incisal restIncisal rest

More applicable to More applicable to mandibular caninemandibular canine

-Definite support with little loss of-Definite support with little loss of tooth structuretooth structure -Little display of metal-Little display of metal

Incisal Rest Prep.Incisal Rest Prep.

2. 5 mm wide2. 5 mm wide 1. 5 mm deep1. 5 mm deep

Incisal Rest Prep.Incisal Rest Prep. Rounded notch at Rounded notch at

the incisal angle the incisal angle with the deepest with the deepest portion apical to portion apical to the incisal edgethe incisal edge

The notch should The notch should be beveled labially be beveled labially & lingually *& lingually *

Multiple Incisal RestsMultiple Incisal Restso Take advantage of natural Take advantage of natural

incisal faceting.incisal faceting.o Tooth morphology does not Tooth morphology does not

permit other designs.permit other designs.o Can restore defective or Can restore defective or

abraded tooth anatomy.abraded tooth anatomy.o Provide stabilization.Provide stabilization.o May restore or provide May restore or provide

anterior guidance.anterior guidance.

ReferencesReferences

1. 1. McCracken’s Removable McCracken’s Removable Prosthodontics, 11Prosthodontics, 11thth Edition Edition 2005 by McGivney GP, Carr 2005 by McGivney GP, Carr AB. Chapter 5 and 6AB. Chapter 5 and 6

2. 2. Dalhousie continual Dalhousie continual educationeducation

Minor Connectors & Rests

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